1. Field of the Invention
The present invention relates to a high stack factor amorphous metal transformer core, and to a process for constructing a high stack factor amorphous metal transformer core. The process uses high lamination factor amorphous metal ribbon (the term lamination factor is generally used to express the smoothness and uniformity of the ribbon, whereas the term stack factor is applied to cores made from ribbon); that is, amorphous metal ribbon with a highly smooth surface and a highly uniform thickness as measured across the ribbon width. High stack factor amorphous metal ribbon can be efficiently packed, by winding or stacking operations, into compact transformer core shapes. The transformer core can then be clamped, to further reduce overall dimensions, and annealed, to relieve residual mechanical stresses and to generate a desired magnetic anisotropy, without detriment to the final magnetic properties.
High stack factor amorphous metal transformer cores will have smaller core build dimensions, yet will maintain the same core net area, when compared to conventional amorphous metal transformer cores. The smaller core build will result in a smaller amorphous metal transformer core, which, in turn, allows for a reduction in size or quantity of other transformer components. For example, a high stack factor amorphous metal transformer will contain smaller coil windings, will be housed in a smaller tank, and, if used in liquid filled transformers, will be filled with less oil. These factors all contribute to a reduced amorphous metal transformer cost.
2. Description of the Prior Art
Amorphous metal transformer cores can be manufactured by winding a single amorphous metal ribbon, or by winding a package consisting of multiple layers of amorphous metal ribbons, into the shape of an annulus. The annulus is then cut along a radial line, creating a single joint. The annulus can be opened at the joint to accommodate placement of the primary and secondary coils, and then closed to recreate the original annulus shape.
Another approach to manufacturing amorphous metal transformer cores is to cut a single amorphous ribbon, or to cut a package consisting of multiple layers of amorphous ribbons, to predetermined lengths. The cut amorphous metal ribbons are then wrapped around a mandrel, or are stacked and wrapped around a mandrel, to create a tightly wound core form. The individual lengths of the amorphous metal ribbon are wrapped about the mandrel such that the cut ends form a distributed series of joints aligned in a localized region of the core. The core can then be opened, by separating the distributed joints, to accommodate placement of the primary and secondary coils, and then closed to recreate the original wrapped core shape.
U.S. Pat. Nos. 4,734,975, 5,261,152 and 5,329,270 disclose amorphous metal transformer cores constructed from groups of amorphous metal ribbon, cut to predetermined length, and wrapped around a mandrel to form a distributed joint core. These patents are incorporated herein by reference for their teachings as to how to produce amorphous metal transformer cores.
Cores manufactured in these manners, with conventional amorphous metal ribbon, are limited to stacking factors of about 86% or less. Accordingly, cores built with these limitations are much larger than conventional silicon steel transformers, use more amorphous metal, more conductor (copper or aluminum) for the primary and secondary coils, more steel for the tank, and, if used in liquid filled transformers, more oil to fill the tank. These factors all contribute to increased materials usage in transformer manufacturing and increased transformer cost. Manufacturing cost penalties range from 20 to 50% (or more).
In addition, the increased size of the transformer is undesirable in many locations and applications where space is limited. The cost and size penalties limit the number of applications, and hence the market size, for amorphous metal transformers.